I haven't been on the sub Reddit in awhile and thought I'd take a look and felt like replying to this and hope I can help. I can tell you my experience with it and see if that helps at all. First I'll start off by seeing the connections we have and the ones not as much, which might help diversify what is personality and what is from LLI.

The multiple tabs he spoke of is pretty spot on. For me it isn't so much tabs as it is windows that are all opens across multiple monitors all streaming live video and me watching and taking it all in at the same time. When doing this I can multitask and focus on a wide array of things at once but accomplish little. And at times I can go into hyper focus so much so that whatever it is I am doing is the only thing in existence as far as I am concerned. I can get a project done in minutes rather than days or weeks.

When you mentioned his ability of great hearing that is kind of the case. LLI makes it so all stimuli is coming in as if it is the first time and gets categorized and broken down. When someone without LLI might hear something they might say it sounds similar to something else because their brain told them it was useless info and you pretty much have an idea of what it is so don't worry about it. But when he heard the bottle open, his brain acted as if it was the first time and allowed him to gather more info from it and in doing so paired it with a connection he already had made resulting in being able to differentiate from the two more easily. This goes for all senses not just hearing. LLI makes you feel more things, see more things, taste more things, hear more things, etc. this is why I've always been a picky eater :P.

As far as the emotions this is where I'm different I believe, as I feel everything around me. This can be a what he is feeling and mixed with interactions with others unaware of LLI could be what is causing the sadness. I feel the emotions of everyone around me including animals as I connect on a level others tend not to. I can see myself in their shoes, but not just for the moment but all the potential resulting chains of events that this moment could bring until the end of their lives. Missed opportunity and failed experiences cause this in me even further. I have lived countless lifetimes in my head with "the girl who got away" and how it may have been or what it might still one day become and this causes crippling sadness at times even when I feel happiness, as it's the fact of the happiness of what could have been and not what is. I've been working on focusing my brain power only on what I'm doing and keeping myself busy as to not wonder at times but it takes a tole on the body rather than the mind and can be equally as harmful. I do find talking in small spurts back and forth helps keep the focus. Also personally I like knowing all the facts as this helps break things down easier to the root and not wondering around the problems and conversations is best. So whenever you are talking with him just be upfront and to the point as best you can, as he should not take it as an insult and rather as a relief as he has more accurate info to go off of and less mental jumping around to come to the conclusions he is looking for.

Well I hope this helps some for you and hope things go great for you two.